Account for preempting events on the Phrequent list view

Summary: Fixes T5850. Also fixes some logic where the wrong preempting events could be attached during a bulk query.

Test Plan: Phrequent list now shows preemption-aware times.

Reviewers: hach-que, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5850

Differential Revision: https://secure.phabricator.com/D10223